3:45 PM - 4:00 PM
[SCG52-20] Estimations of vertical movements on the long-term (>106 yrs.) based on low-temp. thermochronology: current status and prospects in island arcs
★Invited Papers
Keywords:Thermochronology, Island arc, vertical strain, Fission-track method, (U-Th)/He method, the Southwest Japan Arc
Estimations of strain rates on various spatio-temporal scales, based on Geodesy, Geomorphology, and Geology, play a key role in comprehending the crustal movements. In recent, the understanding of deformation in the Northeast (NE) Japan Arc has been greatly enhanced and deepened by the cross-disciplinary approach of the Crustal Dynamics Project (see also Fukahata et al., 2019; 2020, Jour. Geogra.). As for the thermochronologic researches the authors have conducted, developments of thermochronology in the last 30 years enable to reconstruct uplift/denudation histories of low relief mountains in island arcs (Sueoka et al., 2015, Earth Sci.). We have thus applied the low-temperature thermochronometries, such as fission-track and (U-Th)/He methods (hereinafter, FT and He methods), to the NE Japan Arc along the across-arc traverses, and successfully estimated thermal/denudation histories over geologic (>106 yrs.) timescales (Sueoka et al., 2017, EPS; Fukuda et al., 2019 JAES:X; 2020, EPS). Consequently, contrasts in thermal/denudation histories were identified between fore-arc, volcanic arc, and back-arc regions along the across-arc direction, and the contrasts were commonly observed in the arc-parallel direction. In the world, the NE Japan Arc is one of the most studied island arcs in terms of thermochronology, but is far less studied than continental arcs such as the Andes and/or the Cascade (Fukuda et al., 2021, RADIOISOTOPES). For reconstructing the detailed uplift/denudation processes of island arcs, further thermochronometric investigations will be desirable.
Based on these achievements and contributions in the NE Japan Arc, the authors have started a new thermochronologic study in the Southwest (SW) Japan Arc since 2021. In contrast to a relatively simple geomorphic setting in the NE Japan Arc, the SW Japan Arc has more complex tectonic and/or geomorphic features due to the oblique plate subduction, and the distribution of two uplift zones, i.e., Chugoku and Shikoku mountains. In addition, a limited number of geomorphic studies were performed to estimate the mountain building process of the two mountains (e.g., Tanaka & Suzuki, 2021, Okayama Univ. Earth Sci. Res.), where fluvial terraces are poorly distributed. This fact hence makes it difficult to understand the quantitative uplift/denudation processes in the SW Japan Arc. In this study, thermochronologic investigations of the SW Japan Arc have been progressing by following the methodology we applied to the NE Japan Arc, which will contribute to estimating thermal/denudation histories based on FT and He thermochronometers against the Cretaceous-Paleogene granitoids as bedrock samples along the across-arc traverses. In this presentation, thermochronometric results of the NE Japan Arc will be introduced, and preliminary data and its interpretations in the SW Japan Arc will also be provided.
As described above, recent thermochronometric studies have constrained the vertical movements of island arcs temporally and spatially, and new advances are emerging subsequently to the researches of the NE Japan Arc. On the other hand, the electronic spin resonance (ESR) method (King et al., 2020, Geochron.) and the monazite fission-track method (Jones et al., 2019, Geochron.) have been developed as new ultra-low temperature (<50 degrees Celsius) thermochronometers. Preliminary applications have already been attempted and reported in Japan and overseas so far. If these methods are valid for detecting the movements in the uppermost crust (shallower than 1-2 km), they may contribute to the understanding of the Quaternary tectonics in young orogens like Japan Islands. As researchers involved in thermochronology, we hope that the technological development and application studies of new methods will continuously evolve in the future.
Acknowledgments: This study was supported by the JSPS Grant-in-Aid for Young Scientists (B) (No. 21K14021) and for Scientific Research (C) (No. 21K03730).
Based on these achievements and contributions in the NE Japan Arc, the authors have started a new thermochronologic study in the Southwest (SW) Japan Arc since 2021. In contrast to a relatively simple geomorphic setting in the NE Japan Arc, the SW Japan Arc has more complex tectonic and/or geomorphic features due to the oblique plate subduction, and the distribution of two uplift zones, i.e., Chugoku and Shikoku mountains. In addition, a limited number of geomorphic studies were performed to estimate the mountain building process of the two mountains (e.g., Tanaka & Suzuki, 2021, Okayama Univ. Earth Sci. Res.), where fluvial terraces are poorly distributed. This fact hence makes it difficult to understand the quantitative uplift/denudation processes in the SW Japan Arc. In this study, thermochronologic investigations of the SW Japan Arc have been progressing by following the methodology we applied to the NE Japan Arc, which will contribute to estimating thermal/denudation histories based on FT and He thermochronometers against the Cretaceous-Paleogene granitoids as bedrock samples along the across-arc traverses. In this presentation, thermochronometric results of the NE Japan Arc will be introduced, and preliminary data and its interpretations in the SW Japan Arc will also be provided.
As described above, recent thermochronometric studies have constrained the vertical movements of island arcs temporally and spatially, and new advances are emerging subsequently to the researches of the NE Japan Arc. On the other hand, the electronic spin resonance (ESR) method (King et al., 2020, Geochron.) and the monazite fission-track method (Jones et al., 2019, Geochron.) have been developed as new ultra-low temperature (<50 degrees Celsius) thermochronometers. Preliminary applications have already been attempted and reported in Japan and overseas so far. If these methods are valid for detecting the movements in the uppermost crust (shallower than 1-2 km), they may contribute to the understanding of the Quaternary tectonics in young orogens like Japan Islands. As researchers involved in thermochronology, we hope that the technological development and application studies of new methods will continuously evolve in the future.
Acknowledgments: This study was supported by the JSPS Grant-in-Aid for Young Scientists (B) (No. 21K14021) and for Scientific Research (C) (No. 21K03730).